1. Field of the Invention
The present invention relates to exhaust reburner systems. More specifically, the present invention relates to methods and apparatus for engine reburner systems that decompose pollutants in the exhaust of Otto cycle piston and rotary engines.
While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility.
2. Description of the Related Art
The exhaust from piston and rotary engines contain pollutants that are created due to the inefficient burning process of hydrocarbon based fuels. Partially burned and unburned fuel is thereafter exhausted from the engine, through a muffler and into the atmosphere. Engines are often operated at low temperatures resulting in less than total combustion of all the fuel injected therein. Operation at temperatures insufficient for complete combustion ensures cooler operation and longer life of the engine. Cooler operation is accomplished by operating an engine fuel rich. Consequently, the air-fuel mixture does not contain sufficient oxygen for complete combustion. Although operating an engine at cooler temperatures can produce fewer Nitrogen/Oxygen compound (NO.sub.x) pollutants, the hydrocarbon exhaust count increases dramatically.
Several methods have been employed in the past to reduce the pollutants exhausted from piston and rotary engines. One of these methods employs a particulate trap system in diesel engines to capture hydrocarbons and soot, e.g., carbons. The exhaust from the diesel engine feeds into a trap having at least one ceramic filter contained therein. The ceramic filter is housed within a metal container located at the end of an engine exhaust pipe. The function of the cermanic filter is to remove particulate matter from the exhaust gases.. Located between the ceramic filter and the engine exhaust pipe is a combustion chamber. The combustion chamber includes separate air and fuel input lines. Back pressure in the engine is monitored by an engine pressure sensor. An increase in engine back pressure indicates that the ceramic filter is becoming clogged with particulate matter.
In situations in which dual filter systems are utilized, an automatic transfer device senses the buildup of back pressure in the combustion chamber. The ceramic filters are then automatically switched. Thereafter, a suitable fuel is mixed with air in the proper proportions in the combustion chamber and then ignited. The heat generated in the combustion chamber is utilized to raise the temperature of the ceramic filters and to burn the trapped particulate. The ceramic filters trap and destroy approximately 80% of the soot and hydrocarbon particulate in the engine exhaust. Unfortunately, the carbon monoxide (CO) and NO.sub.x created by the engine and by the particulate trap system is released to the environment as pollutants.
Another method employed to reduce pollutants exhausted from piston and rotary engines employs a catalytic converter. A catalytic converter is typically located within the exhaust line between the exhaust manifold and the muffler of an automobile. It is noted that a catalytic converter cannot be utilized in conjunction with a diesel engine as the dense diesel exhaust mixture of particulate and unburned fuel clogs the catalytic material. Catalytic converters employed with gasoline engines often utilize platinum as the catalytic material. The platinum is extruded into the shape of bundled wires. The extruded platinum chemically reacts with the particulate matter reducing the carbons and hydrocarbons to the base elements of carbon, hydrogen and oxygen. Unfortunately, the extruded platinum is generally inefficient and does not destroy all of the pollutants. Thus, those pollutants exiting the catalytic converter are exhausted to the atmosphere. Further, platinum is very expensive and thus not economical for use in catalytic converter systems.
An example of a method to reduce the level of pollutants exhausted to the atmosphere utilizes an incinerator employed for destroying hazardous and toxic waste on a large scale. The incinerator includes a cylindrical combustion chamber joined by a flat circular plate to a smaller inlet pipe. Fuel nozzles protrude through the flat plate into the combustion chamber. Air and fuel are not premixed but rather are injected into the combustion chamber at the point of flame stabilization. Sudden expansion of air between the inlet pipe and combustion chamber provides the effect of a flame holder. Combustion of the fuel occurs and low (NO.sub.x) levels are produced. Recirculation of the gas and air mixture is employed to ensure total combustion. The heat generated by the combustion is released to the atmosphere through a long hot exhaust tube that completes the decomposition of the hydrocarbon and carbon molecules.
In another example, an incinerator comprises a concentric elongated tubular array with an outer closed tubular housing and an annular tubular heat exchanger in the form of a bundle of spaced open-ended tubes inside the housing. The annular tubular heat exchanger cooperates with a combustion chamber that receives a fuel line, a fluidized waste material line and an ignition system along with a source of heated air. Although each of the incinerators is useful for very large scale destruction of toxic and carcinogenic materials, it is completely impractical for use in reburning the exhaust of piston and rotary engines. Various large scale incinerator devices for destroying hazardous waste are known and by way of example, several embodiments of such devices can be found in U.S. Pat. Nos. 3,074,469, 4,785,748 and 4,915,038.
In a final example, an exhaust gas after-burning system for reducing vehicle air pollution is known. The system includes a reactor for re-oxidizing the unburned components of engine exhaust gases such as hydrocarbons and carbon monoxides. A fuel supply unit and an air supply unit are incorporated in the system for supplying secondary fuel and air, respectively, in controlled quantities to the reactor. The secondary fuel and air supplied to the reactor vary with the engine load. The combustible mixture of the secondary fuel and air is ignited within the reactor by an ignition plug so that the unburned gases of the exhaust are reburned. The fuel supply unit utilizes a check valve to control the flow of fuel to the reactor. The engine exhaust gases and the supplied air are not premixed but are delivered to the inner combustion chamber from opposite ends thereof. Only the combustible air-fuel mixture is directly exposed to the region of the ignition plug. Thus, the efficiency of combustion of the unburned components of the engine exhaust gases is suppressed. An example of an exhaust gas after-burning system for reducing vehicle air pollution can be found in U.S. Pat. No. 3,750,401.
Thus, there is a need in the art for improvements in engine exhaust reburner systems to eliminate the pollutants exhausted from Otto cycle piston and rotary engines.